Devices and methods for enhancing brightness of displays using angle conversion layers

ABSTRACT

Various embodiments of the present invention relate to enhancing the brightness of displays that employ illumination systems. In some embodiments, the illumination systems include light guides, diffractive microstructure, and light-turning features. The diffractive microstructure may be configured to receive ambient light at a first angle and produce diffracted light at a second angle greater than the first angle and greater than the critical angle for of light guide. The light is thereby guided within the light guide. The light-turning features may be configured to turn the light guided within the light guide out of a light guide and onto, for example, a spatial light modulator at near normal incidence.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/369,630, filed Feb. 11, 2009, U.S. Pat. No. 8,040,589 (issue date:Oct. 18, 2011), entitled “DEVICES AND METHODS FOR ENHANCING BRIGHTNESSOF DISPLAYS USING ANGLE CONVERSION LAYERS,” which claims priority under35 U.S.C. §119(e) to U.S. Provisional Application No. 61/028,145, filedon Feb. 12, 2008, entitled “DEVICES AND METHODS FOR ENHANCING BRIGHTNESSOF DISPLAYS USING ANGLE CONVERSION LAYERS,” both of which are assignedto the assignee hereof. The disclosures of the prior applications areconsidered part of this disclosure and are incorporated by reference intheir entireties.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to enhancing brightness ofreflective displays. In some embodiments, devices include alight-turning features and diffractive microstructure.

2. Description of Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY

In some embodiments, an illumination apparatus is provided, theapparatus comprising a light guide that guides light propagating thereinat an angle greater than a critical angle for the light guide and ejectslight from the light guide to provide illumination; diffractivemicrostructure disposed to receive ambient light at a first anglesmaller than said critical angle and to diffract said ambient light toproduce diffracted light at a second larger angle; and light-turningfeatures configured to turn the diffracted light and direct the turnedlight out of the light guide. The second angle may be greater than thecritical angle of the light guide.

In some embodiments, a method of manufacturing an illumination apparatusis provided, the method including providing a light guide that guideslight propagating therein at an angle greater than a critical angle forthe light guide and ejects light therefrom to provide illumination;disposing diffractive microstructure to receive ambient light at a firstangle smaller than said critical angle and to diffract said ambientlight to produce diffracted light at a second larger angle; andproviding light-turning features configured to turn the diffracted lightand direct the turned light out of the light guide.

In some embodiments, an illumination apparatus is provided, theillumination apparatus comprising means for guiding light propagatingtherein at an angle greater than a critical angle for the light guidingmeans and ejecting light from the light guiding means to provideillumination; means for diffracting ambient light received at a firstangle smaller than said critical angle to produce diffracted light at asecond larger angle; and means for turning the diffracted light anddirecting the turned light out of said light guiding means.

In some embodiments, an illumination apparatus is provided, theillumination apparatus comprising a light guide that guides lightpropagating therein at an angle greater than a critical angle for thelight guide and ejects light from the light guide to provideillumination; and an angle converting structure disposed to receiveambient light at a first angle greater than said critical angle and todiffract said ambient light to produce diffracted light at a secondsmaller angle, wherein a refractive index of said angle convertingstructure is less than a refractive index of said light guide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable minor position versus applied voltage forone exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8A schematically illustrates light incident on a display devicewithin the field-of-view of the display device such that light isreflected therefrom to a viewer within the field-of-view of the displaydevice.

FIG. 8B schematically illustrates a display device comprising an arrayof display elements and having a field-of-view that is tilted withrespect to the array of display elements.

FIG. 8C schematically illustrates light incident on a display device atan angle outside the field-of-view of the display device such that thelight is reflected outside the field-of-view of the display device.

FIG. 8D schematically illustrates a display device having an angularconversion layer disposed forward an array of display elements thatredirects light incident on the display device at an angle outside thefield-of-view into an angle more normal to the array of display elementsand within the field-of-view of the display device.

FIG. 8E schematically illustrates a display device having an angularconversion layer forward a plurality of display elements that redirectslight incident on the display device at an angle outside thefield-of-view into a larger (more grazing incidence) angle such that thelight is guided in a light guide forward the array of display elements.

FIG. 9 schematically illustrates an illumination apparatus comprising alight guide forward an array of display elements, diffractivemicrostructure that couples light incident on the display device at anangle outside the field-of-view into so as to be guided in the lightguide, and light turning features that redirect the light guided by thelight guide onto the array of display elements at near normal incidence.

FIG. 10 schematically illustrates an illumination apparatus furthercomprising an artificial light source such as an light emitting diode ora light bar for providing supplemental illumination.

FIG. 11 schematically illustrates the field-of-view of the displaydevice and the angular range for optical modes guided within the lightguide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is directed to certain specificembodiments. However, the teachings herein can be applied in a multitudeof different ways. In this description, reference is made to thedrawings wherein like parts are designated with like numeralsthroughout. The embodiments may be implemented in any device that isconfigured to display an image, whether in motion (e.g., video) orstationary (e.g., still image), and whether textual or pictorial. Moreparticularly, it is contemplated that the embodiments may be implementedin or associated with a variety of electronic devices such as, but notlimited to, mobile telephones, wireless devices, personal dataassistants (PDAs), hand-held or portable computers, GPSreceivers/navigators, cameras, MP3 players, camcorders, game consoles,wrist watches, clocks, calculators, television monitors, flat paneldisplays, computer monitors, auto displays (e.g., odometer display,etc.), cockpit controls and/or displays, display of camera views (e.g.,display of a rear view camera in a vehicle), electronic photographs,electronic billboards or signs, projectors, architectural structures,packaging, and aesthetic structures (e.g., display of images on a pieceof jewelry). MEMS devices of similar structure to those described hereincan also be used in non-display applications such as in electronicswitching devices.

The perceived brightness of reflective displays can depend on availablelighting. In various embodiments of the present invention, anillumination apparatus for front illuminating reflective displayelements is configured to increase the amount of ambient light that isincident on the display elements and reflected therefrom within a usablefield-of-view to the viewer. This illumination apparatus may comprise alight guide, light-diffractive microstructure, and turning features. Thediffractive microstructure diffracts light incident on the illuminationapparatus at an angle outside the field-of-view away from the normal tothe array of display elements such that ambient light outside thefield-of-view may be coupled into the light guide. The light turningfeatures turn this light guided within the light guide to the displayelements at an angle near normal to the array of display elements.Therefore, the amount of ambient light that can be directed at anglesnear normal to the array of display elements and reflected by thedisplay elements at angles near normal to the array (or otherwise withinthe desired field-of-view) can be increased. In various embodiments, thedisplay elements comprise reflective display elements and in someembodiments, the display elements comprise reflective interferometricmodulators.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“relaxed” or “open”) state, the display element reflects a largeportion of incident visible light to a user. When in the dark(“actuated” or “closed”) state, the display element reflects littleincident visible light to the user. Depending on the embodiment, thelight reflectance properties of the “on” and “off” states may bereversed. MEMS pixels can be configured to reflect predominantly atselected colors, allowing for a color display in addition to black andwhite.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical gap with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. The partially reflective layer can be formedfrom a variety of materials that are partially reflective such asvarious metals, semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials.

In some embodiments, the layers of the optical stack 16 are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) to form columnsdeposited on top of posts 18 and an intervening sacrificial materialdeposited between the posts 18. When the sacrificial material is etchedaway, the movable reflective layers 14 a, 14 b are separated from theoptical stacks 16 a, 16 b by a defined gap 19. A highly conductive andreflective material such as aluminum may be used for the reflectivelayers 14, and these strips may form column electrodes in a displaydevice. Note that FIG. 1 may not be to scale. In some embodiments, thespacing between posts 18 may be on the order of 10-100 um, while the gap19 may be on the order of <1000 Angstroms.

With no applied voltage, the gap 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential (voltage) differenceis applied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by actuated pixel 12 b on the right in FIG. 1. Thebehavior is the same regardless of the polarity of the applied potentialdifference.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate interferometric modulators. Theelectronic device includes a processor 21 which may be any generalpurpose single- or multi-chip microprocessor such as an ARM®, Pentium®,8051, MIPS®, Power PC®, or ALPHA®, or any special purpose microprocessorsuch as a digital signal processor, microcontroller, or a programmablegate array. As is conventional in the art, the processor 21 may beconfigured to execute one or more software modules. In addition toexecuting an operating system, the processor may be configured toexecute one or more software applications, including a web browser, atelephone application, an email program, or any other softwareapplication.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. Note thatalthough FIG. 2 illustrates a 3×3 array of interferometric modulatorsfor the sake of clarity, the display array 30 may contain a very largenumber of interferometric modulators, and may have a different number ofinterferometric modulators in rows than in columns (e.g., 300 pixels perrow by 190 pixels per column).

FIG. 3 is a diagram of movable minor position versus applied voltage forone exemplary embodiment of an interferometric modulator of FIG. 1. ForMEMS interferometric modulators, the row/column actuation protocol maytake advantage of a hysteresis property of these devices as illustratedin FIG. 3. An interferometric modulator may require, for example, a 10volt potential difference to cause a movable layer to deform from therelaxed state to the actuated state. However, when the voltage isreduced from that value, the movable layer maintains its state as thevoltage drops back below 10 volts. In the exemplary embodiment of FIG.3, the movable layer does not relax completely until the voltage dropsbelow 2 volts. There is thus a range of voltage, about 3 to 7 V in theexample illustrated in FIG. 3, where there exists a window of appliedvoltage within which the device is stable in either the relaxed oractuated state. This is referred to herein as the “hysteresis window” or“stability window.” For a display array having the hysteresischaracteristics of FIG. 3, the row/column actuation protocol can bedesigned such that during row strobing, pixels in the strobed row thatare to be actuated are exposed to a voltage difference of about 10volts, and pixels that are to be relaxed are exposed to a voltagedifference of close to zero volts. After the strobe, the pixels areexposed to a steady state or bias voltage difference of about 5 voltssuch that they remain in whatever state the row strobe put them in.After being written, each pixel sees a potential difference within the“stability window” of 3-7 volts in this example. This feature makes thepixel design illustrated in FIG. 1 stable under the same applied voltageconditions in either an actuated or relaxed pre-existing state. Sinceeach pixel of the interferometric modulator, whether in the actuated orrelaxed state, is essentially a capacitor formed by the fixed and movingreflective layers, this stable state can be held at a voltage within thehysteresis window with almost no power dissipation. Essentially nocurrent flows into the pixel if the applied potential is fixed.

As described further below, in typical applications, a frame of an imagemay be created by sending a set of data signals (each having a certainvoltage level) across the set of column electrodes in accordance withthe desired set of actuated pixels in the first row. A row pulse is thenapplied to a first row electrode, actuating the pixels corresponding tothe set of data signals. The set of data signals is then changed tocorrespond to the desired set of actuated pixels in a second row. Apulse is then applied to the second row electrode, actuating theappropriate pixels in the second row in accordance with the datasignals. The first row of pixels are unaffected by the second row pulse,and remain in the state they were set to during the first row pulse.This may be repeated for the entire series of rows in a sequentialfashion to produce the frame. Generally, the frames are refreshed and/orupdated with new image data by continually repeating this process atsome desired number of frames per second. A wide variety of protocolsfor driving row and column electrodes of pixel arrays to produce imageframes may be used.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, voltages of opposite polarity than those described above can be used,e.g., actuating a pixel can involve setting the appropriate column to+V_(bias), and the appropriate row to −ΔV. In this embodiment, releasingthe pixel is accomplished by setting the appropriate column to−V_(bias), and the appropriate row to the same −ΔV, producing a zerovolt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows areinitially at 0 volts, and all the columns are at +5 volts. With theseapplied voltages, all pixels are stable in their existing actuated orrelaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. The same procedure can be employed for arrays ofdozens or hundreds of rows and columns. The timing, sequence, and levelsof voltages used to perform row and column actuation can be variedwidely within the general principles outlined above, and the aboveexample is exemplary only, and any actuation voltage method can be usedwith the systems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processes,including injection molding, and vacuum forming. In addition, thehousing 41 may be made from any of a variety of materials, including butnot limited to plastic, metal, glass, rubber, and ceramic, or acombination thereof. In one embodiment the housing 41 includes removableportions (not shown) that may be interchanged with other removableportions of different color, or containing different logos, pictures, orsymbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device. However, forpurposes of describing the present embodiment, the display 30 includesan interferometric modulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna for transmitting andreceiving signals. In one embodiment, the antenna transmits and receivesRF signals according to the IEEE 802.11 standard, including IEEE802.11(a), (b), or (g). In another embodiment, the antenna transmits andreceives RF signals according to the BLUETOOTH standard. In the case ofa cellular telephone, the antenna is designed to receive CDMA, GSM,AMPS, W-CDMA, or other known signals that are used to communicate withina wireless cell phone network. The transceiver 47 pre-processes thesignals received from the antenna 43 so that they may be received by andfurther manipulated by the processor 21. The transceiver 47 alsoprocesses signals received from the processor 21 so that they may betransmitted from the exemplary display device 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. The above-described optimization may beimplemented in any number of hardware and/or software components and invarious configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 of each interferometric modulatoris square or rectangular in shape and attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is square or rectangular in shape and suspended from a deformablelayer 34, which may comprise a flexible metal. The deformable layer 34connects, directly or indirectly, to the substrate 20 around theperimeter of the deformable layer 34. These connections are hereinreferred to as support posts. The embodiment illustrated in FIG. 7D hassupport post plugs 42 upon which the deformable layer 34 rests. Themovable reflective layer 14 remains suspended over the gap, as in FIGS.7A-7C, but the deformable layer 34 does not form the support posts byfilling holes between the deformable layer 34 and the optical stack 16.Rather, the support posts are formed of a planarization material, whichis used to form support post plugs 42. The embodiment illustrated inFIG. 7E is based on the embodiment shown in FIG. 7D, but may also beadapted to work with any of the embodiments illustrated in FIGS. 7A-7Cas well as additional embodiments not shown. In the embodiment shown inFIG. 7E, an extra layer of metal or other conductive material has beenused to form a bus structure 44. This allows signal routing along theback of the interferometric modulators, eliminating a number ofelectrodes that may otherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. For example, such shielding allows the busstructure 44 in FIG. 7E, which provides the ability to separate theoptical properties of the modulator from the electromechanicalproperties of the modulator, such as addressing and the movements thatresult from that addressing. This separable modulator architectureallows the structural design and materials used for theelectromechanical aspects and the optical aspects of the modulator to beselected and to function independently of each other. Moreover, theembodiments shown in FIGS. 7C-7E have additional benefits deriving fromthe decoupling of the optical properties of the reflective layer 14 fromits mechanical properties, which are carried out by the deformable layer34. This allows the structural design and materials used for thereflective layer 14 to be optimized with respect to the opticalproperties, and the structural design and materials used for thedeformable layer 34 to be optimized with respect to desired mechanicalproperties.

Various embodiments of the present invention relate to increasing theamount of light available to display elements of a display device. Incertain embodiments, a display device comprises a plurality ofreflective display elements having a preferred field-of-view from whicha viewer will view image content displayed by the display elements.Improved brightness may be achieved in certain embodiments by increasingthe amount of ambient light output by the display in within thefield-of-view of the device.

In various embodiments described herein, display devices comprise aplurality of reflective display elements such as reflective spatiallight modulators. Reflective interferometric modulators are examples ofsuch reflective spatial light modulators. In certain embodiments, onlylight incident on the display device within the field-of-view of thedisplay device is reflected within the field-of-view of the device.Accordingly, in such embodiments ambient illumination of the displaydevice is generally limited to ambient light incident on the displaydevice within the field-of-view of the device.

FIG. 8A schematically illustrates the situation where light incident ona display device 800 having a field-of-view 830′ is within thefield-of-view of the display device and is reflected from the displaydevice to a viewer 803 at an angle also within the field-of-view of thedevice. FIG. 8A shows a plurality of display elements 801 having a lightguide 802 or other optically transmissive medium disposed forward (onthe viewing side) of the display elements. Light is incident on thelight guide 802 or optically transmissive medium at an angle within thefield-of-view 830′ of the display device.

Although the optically transmissive medium 802 is shown as a singlelayer, in other embodiments, the optically transmissive medium maycomprises a plurality of layers. For example, one or more films orlayers may form part of the light guide 802. Other embodiments mayinclude additional layers in addition to the light guide 802.Alternatively, some embodiments may exclude the light guide 802. In suchembodiments, the optically transmissive medium 802 disposed forward thedisplay elements 801 may comprise, for example, one or more otheroptically transmissive layers such a substrate on which the displayelements are formed, a protective glass or plastic plate or sheet, orone or more other optically transmissive films, layers, sheets, plates,etc. In other embodiments, a substrate on which the display elements areformed, a protective glass or plastic plate or sheet, etc. may also formpart of the light guide 802.

In general, the optically transmissive medium 802 has a first surface805 that defines an interface, which may be an interface between, forexample, air (above or on the viewing side of the first surface 805) andthe optically transmissive medium 801 (below or on a spatial modulatorside of the first surface 805). Alternatively, the interface 805 may bebetween another medium above first surface 805 and the opticallytransmissive medium 801 below first surface 805. In some embodiments,the medium above the first surface 805 is not part of the display device800, wherein in other embodiments, it is.

An incident light ray 810 can be characterized by a first incident angle815 measured with respect to the normal 820 to the surface 805 and tothe array of display elements 801. The incident light ray 810 isrefracted at the surface 805 to produce a refracted light ray 810 acharacterized by a first transmission angle 815 a. The refracted lightray 810 a is reflected at a second surface 825 corresponding to theplurality of display elements 801 to produce a reflected light ray 810b. The reflected light ray 810 b encounters the first surface 805 of thereflecting device at a second incident angle 815 b. The reflected lightray 810 b is again refracted and becomes an output light ray 810 c,characterized by a second transmission angle 815 c with respect to thenormal 820.

A first angular range 830 corresponding to the field-of-view 830′ of thedevice 800 is shown in FIG. 8A. A second angular range 830 acorresponding to the effective field-of-view 830′ within the opticallytransmissive medium 802 is also shown. The second angular range 830 a issmaller than the first angular range 830 due to refraction within theoptically transmissive medium. A third angular range 830 b symmetricalor, in some embodiments, identical to the second angular range 830 a isalso shown displaced to where the ray 810 b is incident on surface 805and exits from the optically transmissive medium 802. A fourth angularrange 830 c symmetrical or, in some embodiments, identical to the firstangular range 830 is also shown at the location where the ray 810 b isincident on surface 805 and exits from the optically transmissive medium802. This fourth angular range 830 c corresponds to the field-of-view830′ of the device 800 and shows whether a given ray of light reflectedfrom the display device is within the field-of-view 830′ of the device.Similarly, these other angular ranges 830, 830 a, 830 b, correspond tothe field-of-view 830′ of the device 800 and are replicated at differentlocations (inside and outside of the optically transmissive medium 802)as a reference to show whether a given ray of light incident on,refracted by, or reflected from portions of the display device 800 iswithin the field-of-view 830′ of the display device. In the embodimentshown in FIG. 8A, these angular ranges 830, 830 a, 830 b, 830 c showwhether the first incident angles 815, the first transmitted angles 815a, the second incident angles 815 b and the second transmitted angles815 c will be viewable upon exiting the device 800. Thus, if a lightray, such as 810 which is within the first angular range 830, it can beexpected that the transmitted light ray 810 a, the reflected light ray810 b, and the output light ray 810 c will be oriented at angles withinthe first angular range 830 a, the second angular range 830 b and thethird angular range 830 c, respectively.

In some instances, the second angular range 830 a and the third angularrange 830 b include substantially the same range of angles. In someinstances, the first angular range 830 and the fourth angular range 830c include substantially the same range of angles. In other instances,the second angular range 830 a and the third angular 830 b and/or thefirst angular range 830 and the fourth angular range 830 c do notinclude substantially the same range of angles. For example, surfaceirregularities, tilted fields-of-view, and/or a plurality of displaydevice components may contribute to such differences in the angularregions.

The field-of-view 830′ and corresponding angular ranges 830, 830 a, 830b, 830 c may vary depending on, for example, the design of the device800, materials used in the device, how a design is used, or externaldevice properties. In some embodiments, one or both of the first angularrange 830 and the fourth angular range 830 c include a range of about 0°from the normal to about 60° or about 0° from the normal to about 180°from the normal. In some embodiments, one or both of the first angularrange 830 and the fourth angular range 830 c include a range of about 0°from the normal to about 60° or about 10° to about 60° from the normal(e.g., from about 0° or 10° from the normal to about 30°, to about 45°,or to about 60° depending, for example, on the usage model of thedisplays). The angular ranges can depend, for example, on factors, suchas display size and viewing distance. In some embodiments, one or bothof the second angular range 830 a and the third angular range 830 binclude a range of about 0° from the normal to about 40° from thenormal. In some embodiments, one or both of the second angular range 830a and the third angular region 830 b include a range of about 0° fromthe normal to about 20° from the normal. In certain embodiments, therange of the second angular range 830 a and/or the third angular range830 b may be less than the range of the first angular range 830 and thefourth angular region 830 c, for example, as a result of refraction. Inother embodiments, the range of the second angular range 830 a and/orthe third angular range 830 b may be greater than the range of the firstangular range 830 and the fourth angular region 830 c depending on theindex of refraction above and below the interface 805. The fourthangular range 830 c may be approximately 1 to approximately 3 times aslarge as the second angular range 830 a. For example, the fourth angularrange 830 c and the second angular range 830 a may be about 80° andabout 41°, respectively; about 60° and about 35°, respectively; about40° and about 20°, respectively; about 20° and about 13°, respectively;or about 10° and about 7°, respectively, in some embodiments.

FIG. 8B shows an embodiment wherein the field-of-view 83W is tilted andnot centered or symmetrical about the normal 820. Similarly, angularranges 830, 830 a, 830 b and 830 c are not centered or symmetrical aboutthe normal 820. Non-symmetric field-of-views 83W may be applicable, forexample, to display devices 800 for viewing at a tilted angle. It willbe understood that embodiments herein are not limited to symmetricviewing cones centered about the normal 820. The second angular range830 a may be mirror images of the third angular range 830 b. (Forexample, if third angular range 830 b includes angles between −35° and45°, second angular range 830 a could include angles between −45° and35°.) Similarly, the first angular range 830 may include angles that aresubstantially mirror images of the fourth angular range 830 d. In otherembodiments, however, these angular ranges 830, 830 a, 830 b, 830 c neednot be mirror images.

FIG. 8C schematically illustrates the situation where light incident ona display device 800 outside the field-of-view 830′ of the displaydevice and is reflected from the display device at an angle also outsidethe field-of-view of the device. Light ray 810, for example, is shownincident on the light guide 802 or optically transmissive medium at anangle outside the field-of-view 830′ of the display device.

FIG. 8C also shows four corresponding angular regions 835, 835 a, 835 band 835 c outside the field-of-view 830′. A first angular region 835, asecond angular region 835 a, a third angular region 835 b, and a fourthangular region 835 c indicate ranges of the first incident angles 815,the first transmitted angles 815 a, the second incident angles 815 b andthe second transmitted angles 815 c, for which light will not be withinthe field-of-view 830′ upon exiting the device. Thus, if a light raysuch as 810 is within the first angular region 835, it can be expectedthat the transmitted light ray 810 a, the reflected light ray 810 b, andthe output light ray 810 c will be characterized by angles within thesecond angular region 835 a, the third angular region 835 b and thefourth angular region 835 c, respectively and not within thefield-of-view 830′.

Further, FIG. 8C shows first and second forbidden angular regions 840 a,840 b. Light from above the interface 805 will not be refracted intothese forbidden angular regions 840 a, 840 b if the index of refractionabove the interface is less than the index of refraction below theinterface. For example, even if incident light ray 810 encountered thesurface 805 at the largest angle possible, refraction would prevent thelight from entering the first device angular region 840 a and thereforefrom being reflected into the second device angular region 840 b.Typically, the angles within the angular regions 835, 835 a, 835 b and835 c outside the field-of-view will be larger than angles within theangular regions 830, 830 a, 830 b and 830 c corresponding to thefield-of-view 830′ of the device 800, and the angles within theforbidden angular regions 840 a and 840 b will be larger than angleswithin the angular regions 835 a and 835 b outside the field-of-view830′ of the device.

In order to, for example, enhance the brightness of the display device800, it can be advantageous to redirect light incident on the displaydevice outside the field-of-view (e.g., in first angular region 835)into the field-of-view 830′ (e.g., into second angular region 830 a,third angular region 830 b, and fourth angular region 830 c). Therefore,more incident (e.g., ambient) light can directed to the viewer 803 uponreflection from of the plurality of display elements 801. FIG. 8D showsa strategy to increase the amount of ambient light collected using anangle converting device 845, such as a diffractive layer. The angleconverting device 845 re-directs light outside the field-of-view 830′ bychanging the direction of the transmitted light rays towards the surfacenormal 820 (e.g., by reflective or transmissive diffraction). In someembodiments, an index of refraction of the angle conversion layer 845comprises a holographic or diffractive layer. Thus, at least some of theincident light (e.g., light ray 810) that would have been within thefirst angular region 835 a outside the effective field-of-view isre-directed, such that the transmitted light (e.g., transmitted lightray 810 b) is within the first angular 830 a inside the effectivefield-of-view. This light is reflected from the array of displayelements 801 into the third angular region 830 b and output into thefourth angular region 830 c within the field-of-view 83W of the displaydevice 800. This light is therefore directed to a viewer 803. Inessence, the first angular range 830 is redefined as a larger angularregion 831. More light can be collected and directed into thefield-of-view 830′, 831 and be used to convey image content to theviewer 803. The display device is thus brighter.

As illustrated in FIG. 8E, various embodiments of the present inventioninclude an angle converting device 850 that re-directs light by changingthe direction of the transmitted light rays away from the surface normal820. The angle converting device 850 may therefore increase the angle ofthe transmitted ray 810 a as measured with respect to the normal 820.For example, the angle converting device 850 receives light ray 810 andtransmits light ray 810 a to be within the first forbidden angularregion 840 a. Thus, in some instances, the light is re-directed to anangle greater than a critical angle, such as for example the criticalangle associated with the boundaries of the light guide 802. This lightis therefore coupled into the light guide 802 so as to be guided thereinby total internal reflection. The light is optically guided in the lightguide 802 via total internal reflection in a customary manner forwaveguides. In certain embodiments, turning features are included toeject light from the light guide 802 at near normal angles. This lightthen reflects from the array of display elements 801 through the lightguide 802 at near normal angles and out of the display device 800 withinthe field-of-view 83W to a viewer 803.

FIG. 9 shows an embodiment of a display device 900 comprising anillumination apparatus 900′ and a plurality of display elements 901 suchas intereferometric modulators. The illumination apparatus 900′ isforward of the plurality of display elements 901 and assists in frontillumination thereof. The illumination apparatus 900′ of the displaydevice 900 may include a light guide or light guide region 902 thatguides light propagating therein (e.g., light ray 920) at an anglegreater than a critical angle for the light guide. The light 920 isejected from the light guide 902, for example, to provide illuminationof the array of display elements 901 rearward of the light guide. Thelight guide 902 may comprise one or more layers and/or components. Theselayers may comprise glass or polymeric material or other substantiallyoptically transparent material. In some embodiments the light guide 902comprises one or more of glass, polycarbonate, polyether or polyestersuch as, e.g., PET, acrylic or acrylate and acrylate polymers andcopolymers including but not limited to polymethymethacrylate (PMMA),styrene-acrylic copolymer, and poly(styrene-methylmethacrylate)(PS-PMMA), sold under the name of Zylar, and other opticallytransmissive plastics although other materials may also be used. In someembodiments the light guide region 902 has a thickness in the range ofbetween about 100 μm and about 1 cm, e.g. between 0.1 mm and 0.4 mm,although the thickness may be larger or smaller. In some embodiments,the light guide region 902 has a thickness of less than about 400 μm,such as, for examples, embodiments in which the light guide does notinclude a substrate. In some embodiments, the substrate is part of thelight guide region 902 and thus the thickness of the light guide region902 may be larger, such as about 100 μm to about 1 cm.

The light guide region 902 may include a substrate 915 in certainembodiments. This substrate 915 may comprise substantially opticallytransmissive material such as for example glass or plastic or othermaterials. As described above, the material may comprise aluminumsilicate or borosilicate glasses although other materials may also beused. For example polycarbonate, polyether and polyesters such as, e.g.,PET or PEN, acrylics or acylates and acrylate polymers and copolymersincluding but not limited to PMMA, poly(styrene-methylmethacrylate)(PS-PMMA) sold under the name of Zylar, and other optically transmissiveplastics may be used. The materials that may be employed, however, arenot limited to those specifically recited herein. The substrate 915 mayhave a thickness between about 0.1 mm and about 1 cm, (e.g. between 0.1mm and 0.4 mm), although the thickness may be larger or smaller. In someembodiments, the substrate 915 may have a thickness sufficient tosupport other layers or films thereon.

The illumination apparatus 900′ may also include light-turning features903. A light-turning layer 905 may comprise a plurality of light-turningfeatures 903. The light-turning features 903 may include, for example,prismatic and/or diffractive features. The light-turning features 903may be shaped and/or oriented to turn light such that light guidedwithin the light guide 902 is directed out of the light guide.Additionally, light-turning features 903 may be shaped and/or orientedsuch that the angle as measured with respect to the normal 920 to thelight guide 902 and/or array of display elements 901 of the turned lightis reduced and is therefore more normal, for example, as compared tolight prior to interacting with the turning features. In someembodiments, the light-turning features 903 may be shaped and/ororiented to increase the amount of light within the field-of-view of thedisplay device 900 and/or to increase the percentage of incident and/orambient light that is output into the field-of-view of the displaydevice. Alternatively, the light-turning features 903 may be shapedand/or oriented to reduce the angular size of the field-of-view of thedisplay device 900. For example, the light-turning features 903 mayassist in concentrating light output or reflected from display device900 into a smaller angular region.

In FIG. 9, the light-turning features are shown as arranged on a layer.This layer forms an upper portion, and in particular, an upper boundaryof the light guide 902. The light-turning features 903 need not bedisposed at an upper portion of the light-guide 902 but may be locatedelsewhere, for example, in the middle or low portions of the light guidecloser to the display elements 901. In some embodiments, thelight-turning features 903 need not be included in a single layer.

In some embodiments the light-turning features 903 are reflective. Lightguided within the light guide region 902 may be turned upon reflectingfrom such light-tuning features 903.

In one example, the light-turning features 903 comprise prismaticfeatures. Such prismatic features may reflect light off of multiplefacets via total internal reflection. FIG. 9 shows an example of suchfacets that form prismatic features. These prismatic features may bedisposed in a film. This film may be substantially opticallytransmissive. In some embodiments, this film comprises a polymericmaterial such as, e.g., PC, PET, or PMMA, although other materials mayalso be used. In some embodiments, the film comprises a UV-curableresins molded on a plastic carrier film, such as, e.g., PC, PET or PMMA.Accordingly, the film may comprise polymeric material such as anoptically transmissive material including but not limited topolycarbonate, acrylics or acrylates and acrylate polymers andcopolymers including but not limited poly(styrene-methylmethacrylate)(PS-PMMA), sold under the name of Zylar, and other opticallytransmissive plastics. The materials that may be employed, however, arenot limited to those specifically recited herein. This film may bebetween about 50 μm and about 500 μm (e.g. 100 μm and about 500 μm)thick or may have a thickness outside this range. In some embodimentsthe light turning features are between about 1 μm and about 50 μm deepand in some embodiments may be between about 0.5 and 50 μm wide althoughthe light turning features may have other sizes in other embodiments.These features 903 have been exaggerated in size in FIG. 9 forillustrative purposes. Likewise the size, shape, arrangement, and othercharacteristics may be different. Moreover, the light-turning features903 may comprise different structures in other embodiments.

The illumination apparatus 900 may also include diffractivemicrostructure, which may be included in a diffractive layer 910. Thisdiffractive layer 910 may comprise one or more diffractive orholographic layers that provide the angle conversion as described abovewith respect to FIG. 8 (e.g. FIG. 8E). The diffractive microstructuresmay comprise surface and/or volume features that form, for example, oneor more surface and/or volume diffractive optical elements or holograms.Such a diffractive layer 910 may be transmissive in certain embodimentsand may operate on light transmitted therethrough. The diffractive layer910 may operate on light incident thereon from forward of the displaydevice 900 and may be customized to operate on light incident from aparticular angle or set of angles such as ambient light incident on theillumination apparatus 900′ at large angles with respect to the normal.As described above, this light may be incident on the illuminationapparatus 900′ and diffractive layer 910 at angles outside thefield-of-view of the device 900.

The diffractive layer 910 may comprise, for example, holographicrecording films or coatings, such as mixtures of acrylates and vinylcopolymers, or other photopolymers. The diffractive layer may include aholographic material such as, for example, a silver halide material, adichromated gelatin material, a photoresist material, and/or aphotorefractive crystal. Other materials may include those described in,for example, J. E. Boyd et al., Applied Optics. vol 39, iss. 14, p.2353-2358 (10 May 2000), references cited therein, and/orwww.hololight.net/materials.html. In various embodiments wherein thediffractive features 910 are surface features, the diffractive layer 910may further comprise a planarized layer and/or a coating positioned overor under the diffractive microstructure. The planaraization layer maycomprise a wet-coated polymeric coating or a spin-on glass in certainembodiments although the material need not be limited to such material.The diffractive layer 910 may be of any suitable thickness, such as, forexample, between about 10 and about 100 microns although values outsidethis range are possible as well.

The diffractive microstructure and/or the diffractive layer 910 may belocated below or rearward of the light-turning features 902 and/orlight-turning layer 905 with respect to incident light on the displaydevice 900. Thus, ambient light may be transmitted through thelight-turning features 902 prior to being received by the diffractivemicrostructure. The diffractive microstructure and/or the diffractivelayer 910 may be configured to receive light at a first angle smallerthan a critical angle for the light guide 902 and to diffract the lightto produce diffracted light at a second larger angle. The first andsecond angles may be measured with respect to the normal. The secondlarger angle may be greater than the critical angle of the light guide902 such that the light is coupled into the light guide so as to bepropagated therein by total internal reflection. In some embodiments,the refractive index of the light-turning layer 905 is similar to or thesame as the index of refraction of the diffractive layer 910. Reflectionof light passing through the interface between the light-turning layer905 and the diffractive layer 910 can thereby be reduced. In otherembodiments the refractive index of the diffractive layer 910 is lowerthan or higher (which, in some embodiments, is advantageous over“lower”) than that of the light-turning layer 905. The light-turningfeatures 902 may be configured such that light traveling from thediffractive layer 910 to the light-turning features 902 is turned to bedirected out of the light guide 902 and/or to reduce the angle withrespect to the normal to the illumination apparatus 900′ or displaydevice 900.

As described above, in some embodiments, the illumination apparatus 900includes a substrate 915. This substrate 915 may provide support for thediffractive layer 910 and/or the light-turning layer, for example duringfabrication or use. The diffractive layer 910 and/or the light-turninglayer 905 may be formed over, for example, deposited on or applied(e.g., laminated) to the substrate 915 or one or more layers formed onthe substrate. In some embodiments, the diffractive layer 910 may beformed over, for example, deposited on or applied (e.g., laminated) tothe substrate 915 or one or more layers formed thereon and thelight-turning layer 905 may be formed over, for example, deposited on orapplied (e.g., laminated) to the diffractive layer 910 or one or morelayers formed thereon. Accordingly, in some embodiments the substrate915 may be located beneath the diffractive microstructure and/or thediffractive layer 910 with respect to incident light. In otherembodiments, the diffractive microstructure and/or the diffractive layer910 is formed below or rearward of the substrate 915. In otherembodiments, the illumination apparatus 900 does not include a substrate915.

In some embodiments the substrate 915 forms part of the light guide 902.In the embodiment shown in FIG. 9, the critical angle for the lower orrearward boundary of the light guide 902 is determined by the interfaceof the substrate 915 and an optical medium rearward of the substrate915. In the embodiment shown in FIG. 9, an air gap 916 is disposedrearward of the substrate and illumination apparatus 900′ and forward ofone or more or an array of display elements 901. The interface betweenthe substrate 915 and the air gap in this embodiment determines thecritical angle for reflection from the lower or rearward boundary of thelight guide 902.

In other embodiments, this gap 916 may be filled with material Likewise,in certain embodiments, one or more layers may be attached to thesubstrate 915 rearward of the substrate and form port of the light guide902. These layers may or may not be part of the light guide region 902depending, for example, on the index of refraction of these layers.

In the embodiment shown in FIG. 9, the critical angle for the upper orforward boundary of the light guide 902 is determined by the interfaceof the light-turning layer 905 and an optical medium forward of thelight-turning 905 or illumination apparatus 90W. In the embodiment shownin FIG. 9, an air layer is disposed rearward of the substrate andillumination apparatus 900′ and forward of an array of display elements901. The interface between the light-turning film 905 and the air inthis embodiment determines the critical angle for reflection from theupper or forward boundary of the light guide 902.

In other embodiments, the light-turning layer 905 is not the uppermostor forwardmost layer. In such embodiments, one or more layers forwardthe light-turning layer 905 may determine the critical angle for theupper or forward boundary of the light guide 902 depending on index ofrefraction. Likewise, in certain embodiments, one or more layers may beattached to the light turning layer forward of the light-turning layer905 and form part of the light guide 902 or define a boundary of thelight guide 902. A planarization layer may be disposed on thelight-turning layer 905. The layer or layers forward the light-turninglayer 905 may or may not be part of the light guide region 902depending, for example, on the respective indices of refraction.

More generally, the critical angle for the upper or forward boundary ofthe light guide 902 may be determined by the interface of the forwardmost layer of the light guide 900 and the optical medium directlyforward of the forwardmost layer. The critical angle for the lower orrearward boundary of the light guide 902 may be determined by theinterface of the rearwardmost layer of the light guide 900 and theoptical medium directly rearward of the rearwardmost layer.

In some embodiments, an isolation layer is disposed between the lightguide region 902 and the plurality of display elements 901. Thisisolation layer, for example, may comprise a material having an index ofrefraction lower than the light guide 902. In the absence of the air gap916 or isolation layer, the light guide 902 may be disposed directly onthe array of display elements 901. In such a configuration, light guidedwithin the light guide 902 may be incident on the array of displayelements 901 may be absorbed.

FIG. 9 shows an example trajectory of a ray of light 920 through theillumination apparatus 900. The light ray 920 enters the illuminationapparatus 900 at the top surface of the light-turning layer 905. Due toa difference in refractive indices, the light beam 920 is refracted asshown by transmitted light ray 920 a. In this example, the light ray 920a is transmitted through the light-turning layer 905 into thediffractive layer 910. The diffractive layer 910 diffracts andre-directs of the light ray 920 a, producing a diffracted light ray 920b directed at an angle 930 from the normal to the display apparatus 900′and one or more or an array of display elements 901. This angle 930 islarger than the angle 925 of an undiffracted ray that would result inthe absence of the diffractive layer 925.

The diffracted light beam 920 b is totally internally reflected at theinterface between the substrate 915 and the air gap 916 to produce thereflected light beam 920 c. The reflected light beam 920 c travelsthrough the diffractive layer 910 into the light-turning layer 905. Thelight-turning features 902 then turn the light, such that the turnedlight beam 920 d has a reduced angle with respect to the normal ascompared to the angle with respect to the normal of the reflected lightbeam 920 c. The turned light beam 920 d is then transmitted through thediffractive layer 910 and the substrate 915 to exit the illuminationapparatus 900 and is incident on the array of display elements 901.Although not shown, the turned light beam 920 d may be reflected fromthe array of display element 901 depending, for example, on the state ofthe reflective light modulators. Accordingly, the turned light beam 920d may be directed out of the display device toward a viewer in adirection near normal to the array of display element 901 and within thefield-of-view of the display device 900. Thus, the diffractive layer 910redirects light from a first set of angles into a second set of anglesand thereby enables ambient light directed into a light guide region tobe redirected into an angle that is guided by the light guide region andotherwise forbidden from being directly accessed by ambient light.

FIG. 10 shows a display device 1000 comprising an illumination apparatus1000′ in which the diffractive layer 910 is separated from thelight-turning layer 905. One or more separation layers 1007 may separatethe diffractive layer 910 and the light-turning layer 905. The one ormore separation layers 1007 is substantially optically transmissive andmay be diffusive in some embodiments. The one or more separation layers1007 may have a refractive index lower than that of the light-turninglayer 905 such that the light-turning layer 905 can guide light therein.The one or more separation layers 1007 may have a refractive indexgreater than that of the diffraction layer 910.

The one or more separation layers 1007 may material selected from thegroup of acrylics, polyesters, polyethers, or cycloolefin polymers. Insome embodiments, for example, the separation layers 1007 may comprisean optically transmissive material such as, e.g., polycarbonate,acrylics or acrylates and acrylate polymers and copolymers including butnot limited polymethymethacrylate (PMMA),poly(styrene-methylmethacrylate) (PS-PMMA), sold under the name ofZylar, and other optically transmissive plastics. In some embodiments,the one or more separation layers 1007 may comprise a pressure sensitiveadhesive. The one or more separation layers 1007 may be of any suitablethickness, such as, for example, between about 1 to about 100 microns(e.g., between about 1 and 30 microns) although values outside thisrange are also possible.

The embodiment shown in FIG. 10 also includes a light source 1002 thatprovides light to the illumination apparatus 1000. The light source 1002may comprise an edge light source, located adjacent to the illuminationapparatus 1000 so as to inject light into an edge thereof. The lightsource 1002 may comprise for example one or more light emitters such asLED and may comprise, for example, a linear array of LEDs. In certainembodiments, the light source 1002 may also comprise a light bar and oneor more emitters disposed to inject light into the light bar.

The separation layer 1007 forms a light guiding region 1004 for thelight emitted from the light source 1002. This light guiding region 1004may comprise, for example, the light-turning layer. Light 1035 from thelight source 1002 may enter the light-turning layer 905 as representedby a first light ray 1035 a and may be guided by totally internallyreflection within the light-turning layer 905, until a light-turningfeature 902 turns the first light ray 1035 a. An example turned lightbeam 1035 b is shown directed to the array of display elements 901.

The separation layer 1007 forms a boundary for the light guiding region1004 for the light emitted from the light source 1002. In the embodimentshown in FIG. 10, the separation layer 1007 optically decouples thelight turning layer 905 from the diffractive layer 910. The separationlayer 1007 may reduce or prevent interactions of the light emitted 1035a from the light source 1002 with the diffractive layer 910.

In some embodiments, the separation layer 1007 is excluded and therefractive index of the light-turning layer 905 is higher than that ofthe diffractive layer 910. In such embodiments the light-turning layer905 may guide light therein via in part by total internal reflectionfrom the interface between the light-turning layer 905 and thediffractive layer 910.

The embodiment shown in FIG. 10 also includes an optical isolation layer1008 disposed between the substrate 915 and the array of displayelements 901. This optical isolation layer 1008 may have an index ofrefraction lower than that of the layer forward of the optical isolationlayer, which in this case is the substrate 915. Although the opticalisolation layer 1008 is shown as a single layer, in other variousembodiments the optical isolation layer comprises a multilayer stack.This optical isolation layer 1008 may comprise for example, acrylic oracrylate and acrylate polymers and copolymers including but not limitedto polymethymethacrylate (PMMA) and poly(styrene-methylmethacrylate)(PS-PMMA), sold under the name of Zylar, fluorine containing polymers,and polycarbonate, other optically transmissive plastics or siliconoxide, although other materials may be used. In some embodiments, theoptical isolation layer 1008 may comprise pressure sensitive adhesive.The isolation layer 1008 may be of any suitable thickness, such as, forexample, between about 1 and about 100 microns or between about 1 andabout 30 microns, although the isolation layer may be thicker orthinner. In another embodiment, the isolation layer 1008 may be in closevicinity of the display element 901, and comprise inorganic materialwith different index than the substrate 915.

In the absence of the isolation layer 1008, light diffracted by thediffractive layer 910 such as ray 920 b may be incident on the array ofdisplay elements 901 instead of or in addition to being reflected as ray920 c toward the light-turning layer 905 where the light such as ray 920d is turned at near normal angles toward the display elements. The light(ray 920 b) prematurely incident on the plurality of display elements901 may be absorbed by the display elements or reflected at anglesoutside the field-of-view of the display device 1000. In certainembodiments, separation layer 1007 forms the lower boundary for thelight from LED, while the isolation layer 1008 forms the lower boundaryfor the “converted” beam by the diffractive layer 910 from the ambientlight 920. In certain embodiments they may be combined. Accordingly, invarious embodiments, the isolation layer 1008 is positioned below thediffractive layer 910. In some embodiments, the substrate 915 maycomprise the isolation layer 1008 or the optical isolation layer may bedisposed elsewhere. Additionally, in some embodiments, a secondsubstrate may be provided between the isolation layer 1008 and thedisplay elements 901. The second substrate may serve to support thedisplay pixels 901, while the substrate 915 may support films attachedto the display.

FIG. 11 schematically illustrates how the illumination apparatus 1000′shown in FIG. 10 can operate. FIG. 11 includes an angular region 1115corresponding to the direction of light within the light guiding region1004 into which ambient light can be coupled in the absence of the angleconversion layer 910. This light, however, is not guided in the lightguiding region 1004 by total internal reflection. The boundaries 1105 ofthis angular region 1115 are defined by the critical angle establishedby the interface between the light-turning layer 905 and the air above.Angles greater than this critical angle 1105 as measured from the normal(z-axis) are generally forbidden or not accessible from air without, forexample, the angle conversion layer 910. This critical angle 1105defining the angular boundary 1105 may be about 20°, about 25°, about30°, about 35°, about 40°, about 45° or about 50° in certain embodimentsalthough the angle should not be so limited.

FIG. 11 also includes an angular region 1120 corresponding to thedirection of light within the light guiding region 1004 that is guidedby the light guide region 1004. Thus, light within angular region 1120totally internally reflects both at the interface between thelight-turning layer 905 and the air above and at the interface betweenthe light-turning layer 905 and the separation layer 1007. Theboundaries 1110 of this region 1120 are defined by the critical angleestablished by an interface between the light-turning layer 905 and theseparation layer 1007 and/or by an interface between the light-turninglayer 905 and the diffractive layer 910 below. Angles greater than thiscritical angle 1110 as measured from the normal (z-axis) are guided bythe light guide region 1004. Light incident at angles greater than thiscritical angle 1110 totally internally reflect at the interface betweenthe light-turning layer 905 and the separation layer 1007. This criticalangle 1110 defining the angular boundary 1110 may be approximately about40°, about 50°, about 60°, about 65°, about 70°, about 75°, or about 80°although the angle should not be so limited.

Arrow 1123 shows the effect of another embodiment of the angleconversion layer 910. Such an angle conversion layer 910 may redirectlight from a first set of angles into a third set of angles and enableambient light directed into the light guide region 1004 to be redirectedinto an angle that is guided by a light guide region 1010 comprising thelight-turning layer 910, the angle conversion layer 910 and thesubstrate 915.

Whether the ambient light turned by the angle conversion layer 910 isdirected into either of the light guide regions 1004, 1010 may bedetermined at least in part by the angle conversion layer. Additionally,the selection of materials and corresponding index of refraction of thelayers within the illumination apparatus 100W, such as the index ofrefraction of the angle conversion layer 910 itself may affect whetherthe light is guided within the light-turning layer 905 alone or isguided within the light-turning layer, the separation layer 1007, theangle conversion layer 910 and the substrate 915 or elsewhere.Alternative configurations are also possible.

A wide variety of different embodiments of the invention are possible.For example, components (e.g., layers) may be added, removed, orrearranged. Similarly, processing and method steps may be added,removed, or reordered. Also, although the terms film and layer have beenused herein, such terms as used herein include film stacks andmultilayers. Such film stacks and multilayers may be adhered to otherstructures using adhesive or may be formed on other structures usingdeposition or in other manners.

In certain embodiments, the light-turning features 903 may comprisedifferent structures and may be diffractive or holographic opticalelements, for example. In various embodiments, the light-turningfeatures 903 may turn light transmitted through the light-turningfeatures. The light-turning features 903, for example, may comprisestransmissive diffractive or holographic layers that redirect light asthe light is transmitted through the diffractive or holographic layer.

In some embodiments the diffractive layer 910 may be disposed forwardthe light-turning features 903. In various embodiments, the diffractivelayer 910 may be reflective.

Still other variations are also possible.

Accordingly, while the above detailed description has shown, described,and pointed out novel features of the invention as applied to variousembodiments, it will be understood that various omissions,substitutions, and changes in the form and details of the device orprocess illustrated may be made by those skilled in the art withoutdeparting from the spirit of the invention. The scope of the inventionis indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

1. A display system, comprising: an array of display elements; and anangle conversion layer overlying the display elements, wherein the angleconversion layer is configured to turn ambient light towards the arrayof display elements such that the turned light is reflected andpropagates away from the display system at angles within a field of viewof the display system, wherein the turned light is incident on the angleconversion layer at angles outside of the field of view of the displaysystem.
 2. The system of claim 1, wherein the angle conversion layerincludes a diffractive microstructure.
 3. The system of claim 2, whereinthe angle conversion layer is a holographic turning layer and thediffractive microstructure includes holographic light turning features.4. The system of claim 3, wherein the holographic light turning featuresare part of a volume hologram.
 5. The system of claim 2, wherein theturned light is incident on the diffractive microstructure from aplurality of directions.
 6. The system of claim 1, wherein the field ofview is within about ±60° of a normal to a first surface of the display.7. The system of claim 6, wherein the field of view is within about ±45°of the normal to the first surface of the display
 8. The system of claim1, wherein the display elements are reflective display elements.
 9. Thesystem of claim 8, wherein the display elements include interferometricmodulators, each interferometric modulator including a surface forreflecting the turned light.
 10. The system of claim 1, furthercomprising: a processor that is configured to communicate with thedisplay elements, the processor being configured to process image data;and a memory system that is configured to communicate with theprocessor.
 11. The system of claim 10, further comprising: a drivercircuit configured to send at least one signal to the display.
 12. Thesystem of claim 11, further comprising: a controller configured to sendat least a portion of the image data to the driver circuit.
 13. Thesystem of claim 10, further comprising: an image source moduleconfigured to send the image data to the processor.
 14. The system ofclaim 13, wherein the image source module includes at least one of areceiver, transceiver, and transmitter.
 15. The system of claim 10,further comprising: an input device configured to receive input data andto communicate the input data to the processor.
 16. A display system,comprising: a plurality of display elements configured to transmitreflected incident light outward from an image-displaying side of thedisplay system to form a displayed image; and a means for turning lightincident on the display system towards the plurality of display elementssuch that the turned light is reflected from the plurality of displaymeans and the reflected turned light propagates away from the displaysystem at angles within a field of view of the display system, whereinthe reflected turned light is incident on the means for turning light atangles outside of the field of view of the display system.
 17. Thesystem of claim 16, wherein the plurality of display elements is aplurality of interferometric modulators.
 18. The system of claim 16,wherein the means for turning light includes a diffractivemicrostructure.
 19. The system of claim 18, wherein the diffractivemicrostructure is a volume diffractive microstructure.
 20. The system ofclaim 16, wherein the means for turning light is a hologram.
 21. Thesystem of claim 16, wherein the field of view is within about ±60° of anormal to a first surface of the display system.
 22. A method formanufacturing a display system, comprising: providing a reflectivedisplay having a reflective layer; and providing an angle conversionlayer on the display, the angle conversion layer including a diffractivemicrostructure configured to turn light incident on the display towardsthe reflective layer such that the turned light is reflected off thereflective layer and the reflected turned light propagates away from thedisplay at angles within a field of view of the display, wherein thereflected turned light is incident on the angle conversion layer atangles outside of the field of view of the display.
 23. The method ofclaim 22, wherein providing the angle conversion layer includesproviding a holographic layer.
 24. The method of claim 22, whereinproviding the angle conversion layer includes attaching the angleconversion layer to the reflective display.
 25. The method of claim 22,wherein providing the reflective display includes forming a plurality ofinterferometric modulators, the interferometric modulators formingpixels of the display.